This invention relates to rollers for gravity, push-operated and powered roller conveyors and more particularly to a unique plastic roller assembly which is primarily adapted for use in sanitary or corrosion-free applications.
Sanitary conveying systems are required for the production of food items, chemical products, medical supplies and pharmaceutical goods, and in other industries. These systems should be noncorroding and easily cleanable to remove contaminants. Sanitary conveyor rollers are frequently washed or steam cleaned and are, therefore, subjected to corrosion-inducing fluids and materials.
Various proposals have been made to provide roller assemblies which are easily cleaned and which will not permit the collection of bacteria-forming contaminants. Typically, these systems include a stainless steel or plastic roller which is closed at both ends. The roller is supported by stub shafts or axles which extend inwardly from the side rails of a conveyor support structure.
An example of one such system may be found in commonly owned U.S. patent application Ser. No. 941,176, entitled CONVEYOR ROLLER ASSEMBLY, filed on Sept. 11, 1978, in the names of Charles C. Frost and Siegfried K. Weis and now U.S. Pat. No. 4,213,523, issued on July 22, 1980. The conveyor roller assembly disclosed therein includes a pair of longitudinally extending side supports between which are supported a plurality of plastic roller assemblies. The roller assemblies each include a tubular roller having a hollow interior and planar ends. The open ends of the tubular rollers are closed with circular plugs. The tubular rollers and plugs are formed from an organic resin such as polyvinyl chloride.
The plugs include a cylindrical hub-like portion having an outer diameter closely matched with the inner diameter of the tubular roller to fit tightly therein. The plugs are secured to the roller tube with an adhesive. The plugs are dimensioned to close and seal the ends of the roller assembly to eliminate cracks or crevices into which contaminants may enter and build up.
Each plug also defines a central opening or blind bore within which a bearing insert is disposed. The insert includes a central opening defined by side surfaces which are curved and annular such that the opening is hourglass-shaped in cross section. The insert is fabricated from a low friction polymeric material different from that of the tubular rollers such as a self-lubricating, acetal homopolymer resinous plastic. The rollers are supported on the conveyor cylindrical stub shafts or axles which extend into the insert openings. Another example of prior sanitary roller constructions employing plastic materials may be found in U.S. Pat. No. 3,931,878, entitled SANITARY ROLLER CONVEYOR and issued on Jan. 13, 1976, to Payne.
During the manufacture of sanitary roller assemblies of the aforementioned type, the tubular rollers are typically cut from lengths of extruded tubes. The extruded tubes have a varying wall thickness and hence a nonconstant internal diameter due to the manufacturing process by which they are formed. Additional steps, therefore, must be taken to insure that the end plug or end cap is properly fitted into the end of the roller to seal the interior and to obtain a concentric relationship with the tube periphery. Typically, the end of the tube should be bored to a constant, concentric internal diameter and chamfered. Further, adhesives must typically be employed to secure and seal the end plugs to the tubular roller. These steps add to the manufacturing problems experienced and hence to the cost of the completed roller assembly.
A need exists for a roller assembly, components therefor and a method of manufacture which results in a sanitary conveyor roller wherein the attachment of an end cap or closure to the tubular roller is strong, reliable, liquid-tight without openings or crevices which could retain materials for the breeding of bacteria and which permits the rapid, economical and easily accomplished assembly of the rollers by relatively unskilled operators with minimal training.